Do regular sea urchins show preference in which part of the body they orient forward in their walk?

Abstract

Regular sea urchins, which have pentaradial symmetry, have been believed to show no preference in which part of the body forward they proceed with. Through use of circular statistics, we show that the regular sea urchin Hemicentrotus pulcherrimus had no preference with respect to what body part, as determined by Lovén’s system, should be anterior in locomotion. The sea urchins, however, preferably proceeded with the body part, which had contacted with the aquarium walls at rest, forward. When the contact part was artificially altered, the body part facing forward in the following proceeding changed accordingly: the animals walked with the part that had contacted last forward. The biological significance of this behavior was discussed in relation to the aggregation formation and homing behavior.

Notes

Acknowledgments

We would like to express thanks to Dr. R. Mizui of Yokohama National University for guiding the habitat of H. pulcherrimus. We are grateful to the staff of Misaki Marine Biological Station for collecting H. pulcherrimus. We would like to express thanks to K. Arita, S. Yogo, and H. Tsurimaki for technical assistance. Supported by the grant-in-aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology, Japan to T.M. (No. 21570075).